Bug 1880433 - Restore previous internal priority of <link rel=preload as=fetch>. r=valentin,necko-reviewers

In bug 1866277 we aligned internal priority of
`<link rel=preload as=fetch>` when `network.fetchpriority` is disabled
with the case of `fetchpriority=auto` (PRIORITY_HIGH), effectively
exposing a behavior change in M124. This commit restores the previous
behavior when `network.fetchpriority` is disabled (PRIORITY_NORMAL)
and instead aligns `fetchpriority=auto` with that value.

Differential Revision: https://phabricator.services.mozilla.com/D201944

testing/web-platform/mozilla/tests/fetch/fetchpriority/support/link-tests-data.js

@@ -149,25 +149,25 @@ const kExpectedRequestsOfLinkPreloadFetch = [
         internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
     },
     {   fileNameAndSuffix: "dummy.txt?3",
-        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
+        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL
     },
     {   fileNameAndSuffix: "dummy.txt?4",
-        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
+        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL
     },
 ];
 
 const kExpectedRequestsOfLinkPreloadFetchDisabled = [
     {   fileNameAndSuffix: "dummy.txt?1",
-        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
+        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL
     },
     {   fileNameAndSuffix: "dummy.txt?2",
-        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
+        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL
     },
     {   fileNameAndSuffix: "dummy.txt?3",
-        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
+        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL
     },
     {   fileNameAndSuffix: "dummy.txt?4",
-        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGH
+        internalPriority: SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL
     },
 ];
 

uriloader/preload/PreloadService.cpp

@@ -163,12 +163,12 @@ class SupportsPriorityValueFor {
 
   static int32_t LinkRelPreloadFetch(const FetchPriority aFetchPriority) {
     if (!StaticPrefs::network_fetchpriority_enabled()) {
-      return nsISupportsPriority::PRIORITY_HIGH;
+      return nsISupportsPriority::PRIORITY_NORMAL;
     }
 
     switch (aFetchPriority) {
       case FetchPriority::Auto:
-        return nsISupportsPriority::PRIORITY_HIGH;
+        return nsISupportsPriority::PRIORITY_NORMAL;
       case FetchPriority::High:
         return nsISupportsPriority::PRIORITY_HIGH;
       case FetchPriority::Low:
@@ -176,7 +176,7 @@ class SupportsPriorityValueFor {
     }
 
     MOZ_ASSERT_UNREACHABLE();
-    return nsISupportsPriority::PRIORITY_HIGH;
+    return nsISupportsPriority::PRIORITY_NORMAL;
   }
 };